#include <stdio.h>
#include <string.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <assert.h>
#include <ctype.h>

#define SEP " "
#define NUM 1024
#define SIZE 128

#define DROP_SPACE(s) do { while(isspace(*s)) s++; }while(0)

char command_line[NUM];
char *command_args[SIZE];

char env_buffer[NUM]; //for test

#define NONE_REDIR  -1
#define INPUT_REDIR  0
#define OUTPUT_REDIR 1
#define APPEND_REDIR 2

int g_redir_flag = NONE_REDIR;
char *g_redir_filename = NULL;

extern char**environ;

//对应上层的内建命令
int ChangeDir(const char * new_path)
{
    chdir(new_path);

    return 0; // 调用成功
}

void PutEnvInMyShell(char * new_env)
{
    putenv(new_env);
}

void CheckDir(char *commands)
{
    assert(commands);
    //[start, end)
    char *start = commands;
    char *end = commands + strlen(commands);
    // ls -a -l
    while(start < end)
    {
        if(*start == '>')
        {
            if(*(start+1) == '>')
            {
                //ls -a -l>>  log.txt --追加
                *start = '\0';
                start += 2;
                g_redir_flag = APPEND_REDIR;
                DROP_SPACE(start);
                g_redir_filename = start;
                break;
            }
            else{
                //ls -a -l > log.txt -- 输出重定向
                *start = '\0';
                start++;
                DROP_SPACE(start);
                g_redir_flag = OUTPUT_REDIR;
                g_redir_filename = start;
                break;
            }
        }
        else if(*start == '<')
        {
            // 输入重定向
            *start = '\0';
            start++;
            DROP_SPACE(start);
            g_redir_flag = INPUT_REDIR;
            g_redir_filename = start;
            break;
        }
        else 
        {
            start++;
        }
    }
}

int main()
{
    //shell 本质上就是一个死循环
    while(1)
    {
        g_redir_flag = NONE_REDIR;
        g_redir_filename = NULL;

        //不关心获取这些属性的接口, 搜索一下
        //1. 显示提示符
        printf("[张三@我的主机名 当前目录]# ");
        fflush(stdout);

        //2. 获取用户输入
        memset(command_line, '\0', sizeof(command_line)*sizeof(char));
        fgets(command_line, NUM, stdin); //键盘，标准输入，stdin, 获取到的是c风格的字符串, '\0'
        command_line[strlen(command_line) - 1] = '\0';// 清空\n

        //2.1 ls -a -l>log.txt or cat<file.txt or ls -a -l>>log.txt or ls -a -l
        // ls -a -l>log.txt -> ls -a -l\0log.txt
        CheckDir(command_line);

        //3. "ls -a -l -i" -> "ls" "-a" "-l" "-i" 字符串切分
        command_args[0] = strtok(command_line, SEP);
        int index = 1;
        // 给ls命令添加颜色
        if(strcmp(command_args[0]/*程序名*/, "ls") == 0 ) 
            command_args[index++] = (char*)"--color=auto";
        // = 是故意这么写的
        // strtok 截取成功，返回字符串其实地址
        // 截取失败，返回NULL
        while(command_args[index++] = strtok(NULL, SEP));

        //for debug
        //for(int i = 0 ; i < index; i++)
        //{
        //    printf("%d : %s\n", i, command_args[i]);
        //}
    
        // 4. TODO, 编写后面的逻辑, 内建命令
        if(strcmp(command_args[0], "cd") == 0 && command_args[1] != NULL)
        {
            ChangeDir(command_args[1]); //让调用方进行路径切换, 父进程
            continue;
        }
        if(strcmp(command_args[0], "export") == 0 && command_args[1] != NULL)
        {
            // 目前，环境变量信息在command_line,会被清空
            // 此处我们需要自己保存一下环境变量内容
            strcpy(env_buffer, command_args[1]);
            PutEnvInMyShell(env_buffer); //export myval=100, BUG?
            continue;
        }

        // 5. 创建进程,执行
        pid_t id = fork();
        if(id == 0)
        {
            int fd = -1;
            switch(g_redir_flag)
            {
                case NONE_REDIR:
                    break;
                case INPUT_REDIR:
                    fd = open(g_redir_filename, O_RDONLY);
                    dup2(fd, 0);
                    break;
                case OUTPUT_REDIR:
                    fd = open(g_redir_filename, O_WRONLY | O_CREAT | O_TRUNC);
                    dup2(fd, 1);
                    break;
                case APPEND_REDIR:
                    fd = open(g_redir_filename, O_WRONLY | O_CREAT | O_APPEND);
                    dup2(fd, 1);
                    break;
                default:
                    printf("Bug?\n");
                    break;
            }
            //child
            // 6. 程序替换, 会影响曾经子进程打开的文件吗？不影响
            //exec*?
            execvp(command_args[0]/*不就是保存的是我们要执行的程序名字吗？*/, command_args);
            exit(1); //执行到这里，子进程一定替换失败
        }
        int status = 0;
        pid_t ret = waitpid(id, &status, 0);
        if(ret > 0)
        {
            printf("等待子进程成功: sig: %d, code: %d\n", status&0x7F, (status>>8)&0xFF);
        }
    }// end while
}













